Enhancement of enzymatic catalysis of Bacillus amyloliquefaciens α-amylase by nonionic surfactant micelles

Some enzymes are considerably more stable when formulated with nonionic surfactants than when formulated with anionic surfactants. The effect of a nonionic surfatant, polyoxyethylene mono-N-dodecyl ether (Brij 35; number of units of ethylene oxide moieties, 23), on the kinetic behavior of hydrolysis of amylopectin with Bacillus amyloliquefaciens α-amylase (BAA) was studied at a temperature of 25°C and a pH of 7.0. The hydrolytic rate was accelerated by the addition of the nonionic surfactant above its critical micelle concentration. Lineweaver-Burk plots for the enzymatic hydrolysis in the absence and presence of the nonionic surfactant at 0.5 to 2.5% (wt/vol) had linear relationships, and the kinetic parameters, K m and k cat were obtained. The value of k cat was increased with an increased concentration of Brij 35, whereas the K m value was approximately constant. Therefore, the increase in k cat contributed to the acceleration of the apparent hydrolytic rate. The interaction of amylopectin with the surfactant was examined by a surface tension measurement, and the result confirmed the corresponding binding between the substrate and the surfactant. A fluorescence analysis due to tryptophan in BAA suggested that BAA bound to the nonionic micelles. The increase in k cat suggested that hydrolytic catalysis at the micellar pseudophase was more efficient than that at the aqueous pseudophase. The enhancement of the catalytic rate contributed to the effective removal of food stains containing starch when BAA was added with Brij 35 in a laundry detergent washing test.